The present invention relates to covers for batteries (e.g., lead-acid starting, lighting and ignition batteries).
During the manufacture of batteries, a particular problem is posed by the design of leadthroughs, for example for terminals and cell connectors, which are tight and remain tight. It has to be possible to manufacture the leadthroughs inexpensively and simply, and said leadthroughs have to withstand the highly creepable electrolyte. For this purpose, lead bushings are usually pressed or injection molded into the battery cover or into the cell walls as terminal leadthroughs.
It is desirable to maintain a fixed seat despite the different coefficients of thermal expansion of metal and plastic. In addition, there are further problems as a result of the presence of acid inside and during battery manufacture.
DE 1 671 999 describes a terminal leadthrough in the form of a lead bushing having labyrinth rings, in which circumferential or interrupted undercuts are provided in the labyrinth rings. The labyrinth rings have antirotation safeguards on their external diameters. The required seal for gas and acid is achieved firstly by the welding of the terminals to the terminal bushes and secondly by the encapsulation of the lower part of the terminal sleeve by injection molding. The sealing action between the plastic and the terminal sleeve is achieved by the labyrinthine configuration with (metallically smooth) surfaces which are as smooth as possible in interaction with the three-dimensional shrinkage of the plastic during the manufacture of the battery covers by injection molding.
DE 42 41 393 C2 has disclosed a terminal for an accumulator, in which the ribs of the labyrinth are configured in a barb-shaped manner. They do not therefore lose their sealing action over a broad temperature interval, even in the case of heating.
In this context, an embedding process has proved itself, in which the plastic injection molding point lies in the vicinity of the terminal leadthrough, with the result that this zone solidifies last and therefore ensures optimum pressing shrinkage of the plastic. In order to give this type of terminal bushing leadthrough a certain resistance against twisting rotation, the terminal bushings are provided on the outside on the surface with a toothing system which is incorporated into the sleeve ring, at the level of the battery.
There is then a problem in that, in the region of the joint or separating line between the plastic and the metal which is situated in each case at the end of the terminal bush labyrinth, three-dimensional shrinkage cannot be ensured. This is true, in particular, for the outwardly oriented surface of the battery cover with the region of the antirotation protection means which is already problematic for two-dimensional sealing shrinkage of the plastic.
The consequence is penetration of acid, even if only brief and limited spatially, in a gap of only micrometers in width, and the acid remaining despite very intensive attempts at cleaning.
If, after installation of the battery into the vehicle, the terminal clamp is placed onto the terminal bushing and screwed for electric contact, acid can penetrate into the basic material brass if water is present, on account of tears in the tin plating of the terminal. This leads to the brass basic body of the terminal clamp being decomposed by the release of zinc.
In order to solve this problem, the terminal bushing labyrinth which is to be injection molded later with plastic can be treated in advance with an adhesion promoter or by a powder coating. However, this leads to higher costs.
Manufacture of this type of a gastight and liquidtight terminal seal of a lead accumulator is disclosed in DE 32 30 628 C1 and DE 1 213 904 A. There, the terminal surface is coated with a sealing substance or an adhesive, onto which rubber is applied.
DE 2 263 409 discloses an accumulator battery having end terminals which are configured in one piece, are placed into a casting mold as an insert and are also injection molded into the plastic of the plastic cover during the injection molding process. The end terminal is provided with a flange for sealing purposes.
It would be advantageous to provide an improved plastic battery cover to provide an improved transition between the plastic and the terminal element. It would also be advantageous to provide a battery that incorporates such a battery cover.